Patch "arm64: entry: fix context tracking for el0_sp_pc" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    arm64: entry: fix context tracking for el0_sp_pc

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm64-entry-fix-context-tracking-for-el0_sp_pc.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 46b0567c851cf85d6ba6f23eef385ec9111d09bc Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@arm.com>
Date: Mon, 15 Jun 2015 16:40:27 +0100
Subject: arm64: entry: fix context tracking for el0_sp_pc

From: Mark Rutland <mark.rutland@arm.com>

commit 46b0567c851cf85d6ba6f23eef385ec9111d09bc upstream.

Commit 6c81fe7925cc4c42 ("arm64: enable context tracking") did not
update el0_sp_pc to use ct_user_exit, but this appears to have been
unintentional. In commit 6ab6463aeb5fbc75 ("arm64: adjust el0_sync so
that a function can be called") we made x0 available, and in the return
to userspace we call ct_user_enter in the kernel_exit macro.

Due to this, we currently don't correctly inform RCU of the user->kernel
transition, and may erroneously account for time spent in the kernel as
if we were in an extended quiescent state when CONFIG_CONTEXT_TRACKING
is enabled.

As we do record the kernel->user transition, a userspace application
making accesses from an unaligned stack pointer can demonstrate the
imbalance, provoking the following warning:

------------[ cut here ]------------
WARNING: CPU: 2 PID: 3660 at kernel/context_tracking.c:75 context_tracking_enter+0xd8/0xe4()
Modules linked in:
CPU: 2 PID: 3660 Comm: a.out Not tainted 4.1.0-rc7+ #8
Hardware name: ARM Juno development board (r0) (DT)
Call trace:
[<ffffffc000089914>] dump_backtrace+0x0/0x124
[<ffffffc000089a48>] show_stack+0x10/0x1c
[<ffffffc0005b3cbc>] dump_stack+0x84/0xc8
[<ffffffc0000b3214>] warn_slowpath_common+0x98/0xd0
[<ffffffc0000b330c>] warn_slowpath_null+0x14/0x20
[<ffffffc00013ada4>] context_tracking_enter+0xd4/0xe4
[<ffffffc0005b534c>] preempt_schedule_irq+0xd4/0x114
[<ffffffc00008561c>] el1_preempt+0x4/0x28
[<ffffffc0001b8040>] exit_files+0x38/0x4c
[<ffffffc0000b5b94>] do_exit+0x430/0x978
[<ffffffc0000b614c>] do_group_exit+0x40/0xd4
[<ffffffc0000c0208>] get_signal+0x23c/0x4f4
[<ffffffc0000890b4>] do_signal+0x1ac/0x518
[<ffffffc000089650>] do_notify_resume+0x5c/0x68
---[ end trace 963c192600337066 ]---

This patch adds the missing ct_user_exit to the el0_sp_pc entry path,
correcting the context tracking for this case.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Fixes: 6c81fe7925cc ("arm64: enable context tracking")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm64/kernel/entry.S |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -517,6 +517,7 @@ el0_sp_pc:
 	mrs	x26, far_el1
 	// enable interrupts before calling the main handler
 	enable_dbg_and_irq
+	ct_user_exit
 	mov	x0, x26
 	mov	x1, x25
 	mov	x2, sp


Patches currently in stable-queue which might be from mark.rutland@arm.com are

queue-4.1/arm64-entry-fix-context-tracking-for-el0_sp_pc.patch